Can an unmanaged switch connect to a managed switch in a campus LAN

[Fespino1]

what would happen if a user connects a netgear switch to one of our managed switches. would that port be disabled as soon as that switch is plugged in? can plugging that switch create a loop? Does the switchport need to be an access port or a trunk in order for this to work (to avoid a loop)? would the PCs get an IP address when connected to the unmanged switch (if this switch is connected to the managed switch)?

[Reza Sharifi · Accepted solution]

what would happen if a user connects a netgear switch to one of our managed switches. would that port be disabled as soon as that switch is plugged in? can plugging that switch create a loop? No, the port will not be disabled and the switch will work fine and the user will get an IP. The manged switch should be configured as an access port.You basically extending the user vlan with the netgear switch, so access port is fine and there is no need for any config on the netgear. It is just a dump device.

HTH

[Joseph W. Doherty]

In addition to what Reza already noted . . .

"can plugging that switch create a loop?"

Just plugging it in, it does not (as already noted by Reza), however, if someone cross connects to ports on the unmanaged switch or connects the unmanaged switch to more than one port of the managed switch, then yes.

"would the PCs get an IP address when connected to the unmanged switch (if this switch is connected to the managed switch)?"

Normally yes, as again already noted by Reza, however some managed switches support optional security features to limit the number of hosts connected on an edge port. Such features, if active, may block more than one (or specific) host from joining the network.

[Giuseppe Larosa]

Hello ,

as noted by @Joseph W. Doherty 

>> however, if someone cross connects to ports on the unmanaged switch or connects the unmanaged switch to more than one port of the managed switch, then yes.

This is the main reason why spanning-tree bpdu guard is enabled in most environments. The unmanaged switch is not an issue by itself, but errors in cabling and lack of knowledge of end users can create bridging loops that can stop a whole site / campus LAN.

Use a cable of a different color for the uplink from the unmanaged switch  and put a label on it.

Hope to help

Giuseppe

[Fespino1]

Thank you!

[Leo Laohoo]

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@Fespino1 wrote:

would that port be disabled as soon as that switch is plugged in

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Is BPDU Guard enabled or not?  If it is not, then the port will continue to function. 

If BPDU Guard is enabled, then is auto-recovery of error-disabled port due to BPDU, enabled or not.  If it is, then the port will continue to function.

[Joseph W. Doherty]

I think (?) unmanaged switches generally don't support any STP variant. If so, BPDU guard setting won't matter.